Short Sale Flip

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Please forgive my ignorance if this is something that has been asked before or if it just seems too basic. In a short sale flip, is there any reason why I have never heard of anyone flipping the house back to the seller after the bank has negotiated a short sale with investor? Is this illegal? If you were to do A-B and B-C transactions, what's to keep the investor (B) from taking title however briefly and then selling the house back to the seller at the reduced price? Thanks.